Molecular Dynamics Simulations of Cluster Impacts on Metallic Targets

Abstract

A modified version of the multiple-interaction code SPUT2 has been used to simulate impacts of 63-atom Cu clusters on six-layer Cu targets.Simulations were carried out with cutoff times of 100 and 500 fs for an incident cluster energy of 63 keV (1 keV/atom).Significant enhancements were observed in the maximum potential and kinetic energies achieved in the early phase of the collision cascade.Some hard collisions yielded atoms with potential energies as high as 92 5 eV (in the CM frame) This is almost twice the energy allowed in an isolated two-body collision.The number of hard collisions per time-step vs potential energy is well-fitted with a decaying exponential, allowing extrapolation to higher energies.These results together with similar results for Al clusters impacting Au targets suggest that non-linear collisional effects cannot explain the high D-D fusion rates seen in Beuhler, Friedlander, and Friedman's recent experiment [l].

Time-of-flight-secondary ion mass spectrometry of NaBF4: a comparison of atomic and polyatomic primary ions at constant impact energy

“…The non-linear phenomena induced within spikes arise due to multiple collisions between recoiling atoms. 11,14 The energy density per unit volume deposited by a polyatomic ion impact is a function of the total energy, the mass of the projectile and target atoms and the number of constituents in the projectile. Several theories on the repercussions of collision spike formation have been offered, most in the physical context of enhanced sputtering.…”

“…8,9,11 Though not discussed in detail, Benguerba et al 8 observed that the yield of molecular fragments increased more rapidly with the mass and complexity of the polyatomic projectile (for instance, Au n , n = 1-5) than did the yield of deprotonated molecular ions. This observation suggests again a dependence of molecular fragment ion yield on the energy density.…”

“…The overlap of recoil cascades leads to the formation of a collision or energy spike. [10][11][12] Recent work has suggested that the energy density, the amount of energy deposited into the solid per unit volume, near the surface, as opposed to the energy loss (dE/dx) is the important parameter for the enhanced yield. 13 At constant bombarding energy, the energy density deposited can be scaled upward by increasing the number of atoms in the projectile; viz.…”